What is the difference between the terms NEO and NEA?The word NEO stands for Near-Earth Object, indicating a small body of the Solar System which can come into the Earth neighbourhood. A broad classification of NEOs distinguishes NECs (Near-Earth Comets) from NEAs (Near-Earth Asteroids), which constitute the vast majority of NEOs.

Who discovered the first Near-Earth Asteroid, and when?The first NEA, (433) Eros, was discovered by Gustav Witt from the Urania Sternwarte Berlin and independently found by Auguste Charlois from the Observatoire de Nice, on 13 August 1898. The discovery circumstances, and the orbit of Eros, turned out to be rather unusual… read the full story athttp://spaceguard.iaps.inaf.it/tumblingstone/issues/num20/eng/eros.htm.

What SSA stands for?SSA is the acronym of ESA's "Space Situational Awareness" programme, whose aim is to "to support the European independent utilisation of and access to space for research or services, through providing timely and quality data, information, services and knowledge regarding the environment, the threats and the sustainable exploitation of the outer space surrounding our planet". More info athttp://www.esa.int/esaMI/SSA/index.html.

What is the difference between the Torino and Palermo scales?The Torino scale is a function of the impact energy and probability of the event, with no reference to the time of impact. In the Palermo scale, the risk posed by a possible impactor is compared to the 'background risk' between now and the time of impact. An account on how the Palermo scale was born can be found at http://spaceguard.iaps.inaf.it/tumblingstone/issues/num11/eng/main.htm.

Why the word "keyhole" is used in NEO jargon?Even if an asteroid misses the Earth, it can come back and hit our planet in a subsequent "return". Whether this happens or not depends on the object passing through well-defined regions of space called "keyholes", where the gravitational deflection imparted on the object is exactly right to put it into a future collision course. A detailed explanation can be found at http://spaceguard.iaps.inaf.it/tumblingstone/issues/num20/eng/keyhole.htm.